Houghton, P. (2002). Nine descents of the spirit: Towards inner harmony. Jessica Kingsley.
Lua i Stíl Chicago (17ú heag.)Houghton, Peter. Nine Descents of the Spirit: Towards Inner Harmony. London ; Philadelphia: Jessica Kingsley, 2002.
Lua MLA (9ú heag.)Houghton, Peter. Nine Descents of the Spirit: Towards Inner Harmony. Jessica Kingsley, 2002.
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